TWI411694B - Adhesive, hermetic oxide films for metal fluoride optics method of making same - Google Patents

Abstract

The invention is directed to single crystal alkaline earth metal fluoride optical elements having an adhesive, hermetic coating thereon, the coating being chemically bonded to the surface of the metal fluoride optical element with a bonding energy ≧4 eV and not merely bonded by van der Walls forces. The materials that can be used for coating the optical elements are selected from the group consisting of SiO2, F—SiO2, Al2O3, F—Al2O3, SiON, HfO2, Si3N4, TiO2 and ZrO2, and mixtures (of any composition) of the foregoing, for example, SiO2; HfO2 and F—SiO2/ZrO2. The preferred alkali earth metal fluoride used for the optical elements is CaF2. Preferred coatings are SiO2, F—SiO2, SiO2/ZrO2 and F—SiO2/ZrO2.

Description

Adhesive and hermetic oxide film for metal fluoride optical element and method of producing the same

The present invention claims priority to U.S. Patent Application Serial No. 12/156,429, filed on May 29, 2008.

The present invention relates to a metal fluoride optical element having an adhesive, hermetic oxide film and a method of manufacturing the film and the optical element. In particular, the present invention relates to alkaline earth metal fluoride optical elements having vermiculite and doped vermiculite films, and methods of making the films using plasma ion assisted deposition (PIAD).

The deposition of optical films is a technique known in the art and there are several different methods or techniques for depositing such films. In the method used, it is necessary to perform in vacuum such as (1) conventional deposition (CD), (2) ion assisted deposition (IAD), (3) ion beam spraying (IBS), and (4) plasma ion assist. Deposition (PIAD).

In the conventional deposition (CD) method, the material to be deposited is heated to a molten state by resistance heating or electron impact, and heating must be performed on the substrate on which the thin film is to be deposited. When the material melts and evaporates, the film condenses on the surface of the substrate. Some of the evaporation agent dissociation occurs at the temperature of the molten material used in this method. Although such dissociation is not a problem when depositing elemental materials (such as elemental aluminum, silver, nickel, etc.), problems occur when the deposited material is a mixture (such as SiO ₂ , HfO ₂ ). In the case of oxide materials, a small amount of oxygen is mixed into the combustion chamber during deposition, and attempts to restore stoichiometry are so-called reactive deposition. The film of the CD method is generally porous and lacks sufficient kinetic energy (surface mobility) to overcome surface energy (adhesion) during deposition. The film growth is usually columnar (K. Gunther, Applied Optics, Vol. 23 (1984), pp. 3806-3816), and as the direction of the source increases, the porosity increases as the thickness of the film increases. In addition to high film porosity, other problems encountered with CD deposited films include uneven refractive index, excessive top surface roughness, and weaker absorbency. Although there are some slight improvements by adjusting the deposition rate and increasing the substrate temperature during deposition. However, the overall consideration of the final product illustrates that CD technology is not suitable for use in high quality optical components such as telecommunications components, filters, laser components, and sensors.

The ion-assisted deposit (IAD) is similar to the CD method described above. The added property is that during the deposition process, the film is deposited by the energy ion impact of an inert gas (such as argon), plus some ionized oxygen (oxide). Examples of films generally require improved stoichiometry of the film). Although the energy of the ions is usually in the range of 300 eV to 1000 eV, the ion current at the substrate is low, usually several microamperes/cm ² . (Therefore, IAD is a high voltage, low current density process). The impact can be used to transmit momentum to the deposited film, providing sufficient surface mobility to overcome the surface energy to produce a dense, smooth film. It also improves the non-uniformity and the transparency of the deposited film, and the IAD method does not require or rarely requires heating of the substrate.

The ion beam spray (IBS) method directs an energy ion beam (eg, argon ions in the range of 500 eV to 1500 eV) to a target material, typically an oxide material. The kinetic energy transmitted during impact is sufficient to spray the target material to the substrate where it is deposited as a smooth, dense film. The sprayed material reaches the substrate with high energy and may have hundreds of electron volts, resulting in a high packing density and smooth surface, but the high absorption of the deposited film is a common by-product of the IAD process. Thus, the IBS process also includes IAD sources to improve stoichiometry and absorption. Although the IBS process is an improvement of CD and IAD, IBS still has some problems. These problems in the IBS deposition process include: (1) the deposition process is very slow; (2) more experimental techniques than the production process; (3) there are few existing IBS settings, usually the remnants of the telecommunications foam, one or The two machines are operated by a small work team; (4) the substrate capacity is quite limited; (5) the uniformity of deposition on the substrate may become a limitation, thus affecting product quality and causing high abandonment rate; (6) when the target is corroded The uniformity of the deposited film will change to cause further quality problems and frequent target changes and associated time and cost; and (7) the energy of the impact is quite high leading to the dissociation of the deposited material, and thus the absorption.

Plasma ion assisted deposition (PIAD) is similar to the IAD method described above except that plasma ion assisted deposition delivers momentum to the deposited film through a low voltage but high current density plasma. Typical bias voltages range from 90V to 160V, while current densities range from milliamps/cm ² . Although PIAD instruments are commonly used in the precision optics industry and have also been used to deposit thin films, PIAD still has some problems, especially with regard to the uniformity of deposited films. The deposition of the PIAD is described in U.S. Patent Application Serial No. 11/510,140, the disclosure of which is incorporated herein by reference.

ArF excimer lasers have been selected for use in lithography industrial illumination sources, and are used in semiconductor manufacturing to mass produce patterned germanium wafers. As semiconductor processing progresses from 65nm to 45nm or less, lithography is also faced with an ever-improving resolution, throughput, and stability. Therefore, the expectations and requirements for aligning molecular laser components have also increased. Alkaline earth metal fluoride (CaF ₂ , MgF _{2 ,} etc.) optical crystals, especially CaF ₂ , are the best optical material for manufacturing ArF laser optical components due to their excellent optical properties and high design gap energy. However, the polished but uncoated CaF ₂ surface degrades after millions of pulses at 193 nm fluxes of ~40 mJ/cm ² or more. Some solutions have also been provided to extend the life of polished CaF ₂ components for use with excimer laser systems. These include improved surface finish quality, SiO ₂ thin layer vacuum deposition of F coatings as described in U.S. Patent Nos. 7,242,843 and 7,128,984. However, the semiconductor industry continues to demand higher performance from excimer laser sources, so the power and repetition rate of excimer lasers have increased from 40W to 90W in each of these years, from 2KHz to 6KHz. According to the development of excimer laser technology, the laser power and repetition rate will be further increased to 120W and 8KHz. The increase in power and repetition rate challenges the life of existing laser optics. Due to this increase in power and repetition rate, we will consider the formation of bubbles observed in accelerated laser damage tests, such as CaF ₂ optics using F-SiO ₂ coatings operating at higher power and repetition rates. Causes early failure of optical components. For use in high power and repetition rate laser systems, there is a need to improve the environmental stability of F-SiO ₂ coating CaF ₂ optical components, especially in the case of high humidity.

Therefore, in view of the high power and repetition rate, the industry has become more And, new processing methods or improvements are needed in the current processing. In particular, there is a need for a process that can produce smooth and dense film coatings on metal fluoride optical components, as well as a method of removing bubble formation when such components are used in high power and repetition rate laser systems.

The invention relates to a single crystal alkaline earth metal fluoride optical element, which has adhesiveness and airtight coating film, and the coating film is chemically linked to the surface of the alkaline earth metal fluoride optical element with a link energy of >4 eV, and not only De Valle chain. The material that can be used to coat the optical element can be selected from the group consisting of SiO ₂ , F-SiO ₂ , Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ N ₄ , TiO _{2 ,} and ZrO ₂ , and A group consisting of a mixture of (any component), such as non-limiting SiO ₂ ; HfO ₂ and F-SiO ₂ /ZrO ₂ . In one embodiment, with the alkaline earth metal fluoride optical elements are CaF _2. In another embodiment, the coating material is SiO ₂ and F-SiO ₂ .

In one embodiment, the invention relates to a method of making an adhesive and airtight coating film on an alkaline earth metal fluoride optical component. The method comprises the steps of: providing a vacuum chamber in which an optical element made of a single crystal of alkaline earth metal fluoride is provided, the element being placed on a rotatable plate; at least one selected source of coating material is provided , or a mixture of coating material sources, and evaporating the material using an e-beam to provide a coating material vapor flux that passes from a source of material to the optical element in a mask of a selected shape; provided from a plasma source a plasma ion; rotating the element at a predetermined rotational frequency f; and depositing a coating material on the surface of the optical element as a deposited film, and impinging on the element by a plasma ion during the deposition process, thereby forming adhesion on the element and Airtight film. The film is chemically linked to the surface of the element with a chain energy of ≧4 eV; the alkaline earth metal fluoride is selected from the group consisting of MgF ₂ , CaF ₂ , BaF ₂ , SrF ₂ , and at least two alkaline earth metal fluorides. a mixture; the mask is selected from the group consisting of a partial mask and a reverse mask. In a preferred embodiment, the mask is a partial mask.

The present invention further relates to an optical element having an adhesive film and a hermetic coating film. The optical element is a molded optical element made of a single crystal of alkaline earth metal fluoride, and a coating film is chemically linked to at least one light transmitting surface of the element, and the coating film is bonded to the surface of the element by a e4 eV chain energy. . The alkaline earth metal fluoride single crystal material is selected from the group consisting of MgF ₂ , CaF ₂ , BaF ₂ , SrF ₂ , and a mixture of at least two alkaline earth metal fluorides. In a preferred embodiment, the optical element is made of a single crystal CaF ₂ . The coating material is selected from the group consisting of SiO ₂ , F-SiO ₂ , Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ N ₄ , TiO ₂ and ZrO ₂ , and a mixture of the foregoing materials. Group. The film thickness of the optical element ranges from 20 to 200 nm. In a preferred embodiment, the thickness ranges from 50 to 150 nm. In one embodiment, the optical element is a CaF ₂ optical element. In another embodiment, the coating material on the optical element is SiO ₂ and/or F-SiO ₂ .

11‧‧‧vacuum room

12‧‧‧Optical components

14‧‧‧ mask

15‧‧‧Steam flux

16‧‧‧e-beam

17‧‧‧ Target

18‧‧‧ Plasma source

19‧‧‧ Plasma

20‧‧‧Deposition device

22‧‧‧Component holder

40‧‧‧Chemical link interface

41‧‧‧Components/Substrates

42‧‧‧film

44‧‧‧Substrate

45‧‧‧Background

46‧‧‧ bubbles

100‧‧‧Components/Substrates

Figure 1 is a schematic illustration of the surface of CaF ₂ .

2 is an optical image showing the early failure of a prior art F-SiO ₂ coated CaF ₂ optical element due to bubble formation after a 40 M pulse at 70 mJ/cm ² and 3 KHz with a 193 nm laser.

3 is an SEM cross-sectional image of a prior art F-SiO ₂ coated CaF ₂ optical element resulting in premature failure due to bubble formation under 193 nm laser illumination.

Figure 4 schematically shows the interface of the chemical bonding of the CaF ₂ substrate to the SiO ₂ film.

Figure 5 is a schematic illustration of the smoothing of the plasma in situ during the deposition of the SiO ₂ film on the CaF ₂ optical element.

Figure 6 shows the refractive index of the PIAD SiO ₂ film as a function of the momentum transfer of the plasma.

Figure 7 shows the effect of plasma smoothing on the deposition of a 60 nm thick SiO ₂ film from a standard PIAD process.

Figure 8A is an AFM image of a PIAD deposited F-SiO ₂ film having plasma smoothing in situ and after deposition in accordance with the present invention.

Figure 8B is an AFM image of a PRED deposited F-SiO ₂ film that has not been polished in situ.

Figure 9A is a refractive index depth profile of a PIAD deposited F-SiO ₂ film having a plasma smoothed in situ.

Figure 9B is a refractive index depth profile of a PIAD deposited F-SiO ₂ film having no plasma smoothing in situ.

Figure 10 is an optical image showing the CaF ₂ optical element of the adhesive and hermetic F-SiO ₂ coating of the present invention having no premature failure after 40 M pulse irradiation at 193 nm laser at 700 mJ/cm ² and 3 KHz.

Figure 11 is a SEM cross-sectional image of the adhesive and hermetic F-SiO ₂ coating deposited on a CaF ₂ optical element after exposure to a 40 M pulse at a 193 nm laser at 700 mJ/cm ² and 3 KHz.

This invention relates to improved coated optical components useful in high power and repetition rate laser systems, and to methods of making such optical components. Examples of such optical elements include, but are not limited to, lenses, partial and total reflection mirrors, and windows made of alkaline earth metal fluoride. CaF ₂ is the best metal fluoride for this component.

The method of the present invention can be used to prepare optical components having an adhesive and airtight coating film. The invention is particularly suitable for use in coatings and optical elements prepared from single crystals of alkaline earth metal fluorides such as MgF ₂ , CaF ₂ , BaF ₂ , SrF ₂ , and mixtures of such metal fluorides such as (Ca, Sr) Element made of F ₂ . The material of the coating film may be selected from a mixture comprising SiO ₂ , Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ N ₄ , TiO ₂ and ZrO ₂ , and the previous (any component) The group formed is, for example, non-limiting SiO ₂ ; HfO ₂ and F-SiO ₂ /ZrO ₂ and SiO ₂ /ZrO ₂ . Here, SiO ₂ and F-SiO ₂ can be used as exemplary coating materials, and CaF ₂ can be used as an exemplary optical element/substrate.

The present invention describes three important factors as described herein to achieve the objectives of a fluoride optical element, particularly a CaF ₂ surface, an adhesive and a hermetic oxide coating. It includes:

1. The adhesion of the film is strengthened by the formation of a chemical bond between the interface of the CaF ₂ crystal substrate and the oxide film, rather than the formation of a van der Waals chain. At the interface between the CaF ₂ substrate and the oxide film, the strength of the chemical chain is 100x stronger than that of the Van der Waals, and the oxide film may be a non-limiting SiO ₂ -based film. This results in a strong adhesion to the surface of the alkaline earth metal fluoride optical element (such as a lens made of a single crystal CaF ₂ ) and hermetically seals the film coating on the crystal surface.

2. Enhance the packing density of the film by increasing the momentum transfer of the plasma.

3. Remove the defects of the coating film point and improve the smoothness of the film by the masking technique by smoothing the in-situ plasma.

Strengthen film adhesion:

Figure 1 shows the surface link structure of the CaF ₂ crystal, and the dotted line 40 shows the CaF ₂ interface where the deposited film is located. The formation of the SiO ₂ film on the surface of CaF ₂ is a mechanism of physical vapor deposition (PVD) to generate thermally evaporated SiO ₂ or F-SiO ₂ by electron beam irradiation, which is transported by steam to a CaF ₂ substrate in a high vacuum environment, and Physical absorption on the surface of CaF ₂ . Interaction between SiO ₂ and CaF ₂ film to the substrate is by the van der Waals Controls Waals forces. The estimated van der Waals chain energy of the SiO ₂ -CaF ₂ interface is ~0.04 eV, compared with the Ca-O-Si chain energy of >4 eV (more than the 2nd power of the Van der Waals chain energy 10). It is very weak. This weak interface link can explain the typical early failure of bubble formation in the CaF ₂ optical element of the F-SiO ₂ coating at 193 nm laser radiation. For example, Figure 2 shows an optical image of the early failure of the CaF ₂ optical element of the F-SiO ₂ coating due to bubble formation after a 40 M pulse at a flux of 70 mJ/cm ² due to the use of a 193 nm laser operating at a repetition rate of 3 KHz. . 3 shows an SEM cross-sectional image of the element 41 of the F-SiO ₂ coating as indicated by the brackets, and a bubble 46 formed by the SiO ₂ film 42 peeling off from the CaF ₂ substrate 44 when the optical element is subjected to the aforementioned irradiation (black hump) ). The area of No. 45 is that the background is due to the surface on which the coated CaF ₂ element/substrate 41 is placed, and the white line above the F-SiO ₂ coating film is an artificially generated reflection upon SEM photography, not because of the coating film and/or the substrate. Any defects. The white line is because of the reflection from the edge of the coated article as the edge of the coated article falls to the background where the article is parked. With respect to the bubble formation shown in Figures 2 and 3, Figures 10 and 11 discussed below show a CaF ₂ optical element having an adhesive and hermetic SiO ₂ film coating in accordance with the present invention, passing through 40 M at 70 mJ/cm ² and 3 KHz. No film failure will be shown after the second pulse.

Figure 4 shows the chemically bonded interface 40 of the SiO ₂ film and the CaF ₂ substrate, producing an apparent amount of Ca-O-Si chain. J.Wang et al.'S "Extended lifetime of fluoride ^{optics", 39 th Boulder Damage Symposium, Proc.SPIE} , Vol.6720 672001 (2007) reported that under the impact of Ar plasma, fluorine atoms can easily consume ₂ from the surface of CaF. By inserting oxygen into the Ar plasma, the fluorine vacancies can be occupied by oxygen, with a bridging function that chemically bonds the Ca and Si atoms to create a strong film that adheres to the CaF ₂ substrate.

The process of fluorine consumption and oxygen substitution is controlled by means of a masking technique as shown in Figure 5, where the alpha and beta regions correspond to the shaded and non-shaded regions of the mask, respectively. Figure 5 shows a deposition apparatus 20 having a vacuum chamber 11 in a rotatable element holder 22 on which an optical element 12 to be coated is placed, illuminating the e-beam 16 to a target 17 to produce a vapor flux 15 Deposited on the component 12 by a mask 14. There is also a plasma source 18 that produces a plasma 19. The rotatable element holder 22 has an opening through the holder element for placing the optical element 12 such that only one side of the optical element is coated. In the early stages of film deposition, the plasma only impacts the alpha region of the surface of the CaF ₂ substrate, while the plasma ions in the beta region interact with the deposited SiO ₂ molecules (or F-SiO ₂ ). Fluoride consumption and oxygen substitution occur in the alpha region. In the beta region, Ar/O ₂ continuously collides with the deposited SiO ₂ film to form a Ca-O-Si chain. The coating treatment of the enhanced interface chain can be illustrated by the momentum transfer of each deposited atom P, which is the sum of the kinetic energy transmitted in the alpha zone (P _α ) and the beta zone (P _β ), in units of (aueV) ^0.5 , during the coating period is

Wherein V _b is a bias voltage; J _i and m _i are plasma ion fluxes in units of ions/(cm ² sec) and masses in au; R is a deposition rate in nm/sec; e is the charge; k is the unit conversion factor; n _s is the surface atomic density of CaF ₂ in atom/cm ² ; and α and β are the range of the vapor flux relative to the shaded and non-shaded areas in the center of the rotatable plate Rotate at a frequency f of 4 to 36 rpm. Adjusting the shape and height of the mask, the Advanced Plasma Source (APS) parameters and the plate's rotational frequency allow us to control the amount of kinetic energy transferred by fluorine consumption and plasma-assisted deposition separately. In contrast, the mask height is above the target 17 and below the plasma 19, as shown in FIG. For a particular shape mask, the higher the mask position, the more fluorine is consumed at the interface. Adhesive and hermetic films, such as SiO ₂ films, can be deposited on the fluoride optics using a "partial mask" method, as shown in Figure 5, or as described in commonly-owned U.S. Patent Application Serial No. 11/510,140. "Reverse mask", rather than the general mask used in industry, and by adjusting the APS parameters and the rotation frequency, we can ensure that sufficient ion impact of the deposited film is achieved, so that the deposited film and CaF ₂ optics are deposited. A chemically linked chain is formed between them. The shape of the mask used in carrying out the invention is mainly determined by the ratio of α / β and should be between 1 and 4 (1 ≦ α / β ≧ 4). The "general mask" has no opening through the mask, directly above the target 17; and the reverse mask described in U.S. Patent Application Serial No. 11/510,140 has an opening through the mask. When the "partial mask" shown in Fig. 5 is used, the ratio of α/β should be in the range of 1-4.

Increase film packing density:

When the surface of CaF ₂ is covered by a nanometer, for example, 1-5 nm SiO ₂ film, the deposition process enters the plasma-assisted deposition and the in-situ plasma smoothing system. This process can still be illustrated by equation (1), where P _α and P _β represent in situ plasma smoothing and plasma assisted deposition. According to Equation (1), the amount of the deposited film is applied to the plasma momentum transfer is defined as _P β

We also understand that the refractive index of amorphous SiO ₂ films is directly related to the film packing density when maintaining the correct stoichiometry (see J. Wang et al., "Elastic and plastic relaxation of densified SiO ₂ films", Applied Optics, Vol. 47, No. 13, pp C131-C134). Figure 6 shows the refractive index (solid line) of the SiO ₂ film at a wavelength of 193 nm as a function of the kinetic energy transfer P _β described by equation (2). The refractive index of the bulk fused vermiculite is also plotted in Figure 6, with a dashed line as a comparison. The refractive index of the SiO ₂ film struck by a small amount of plasma is lower than that of the main body, indicating that the film packing density is smaller than that of the main body. The increased momentum transfer of the plasma can produce a film having a higher refractive index than the bulk material. In the case of the SiO ₂ film, the momentum transfer amount of the plasma is 250 (aueV) ^0.5 , which corresponds to the film packing density close to the main body. According to the present invention, the amount of momentum momentum transmission can be further increased to 280 (aueV) ^0.5 . Therefore, the film packing density is larger than that of the host material to form a denser SiO ₂ film.

Smoothing of the original plasma:

In addition to interface strength and film packing density, it is also important to eliminate the formation of coating film defects during film deposition processing, and to replicate the polishing scratches on the substrate surface. This goal can be achieved by using plasma smoothing techniques. The plasma smoothing effect can be confirmed by prolonged plasma treatment in standard PIAD (plasma ion assisted deposition). Figure 7 shows the change in surface root mean square (RMS) roughness of a 60 nm SiO ₂ film as a function of plasma treatment. The RMS value was obtained by AFM measurement. The RMS of the uncoated substrate (labeled "substrate") was 0.40 nm. After standard PIAD process (i.e., ^{_{P β = 250 (aueV) 0.5}} ) film is deposited 60nm SiO ₂ (labeled "post-deposition"), a surface RMS increased 0.71nm. A 1 minute plasma smoothing (labeled "PS_1 points") reduces the RMS to 0.51 nm. A 3 minute plasma smoothing (labeled "PS_3 points") reduced the RMS to 0.42 nm. Figures 8A and 8B show AFM images of a 60 nm SiO ₂ thin layer before and after 3 minutes of plasma smoothing (Figure 8A) and after (Figure 8B). This result indicates that the film size characteristics are not altered due to the interaction of the plasma and the deposited film surface, significantly reducing the high spatial frequency structure.

The interaction of the plasma and SiO ₂ deposition surfaces continues in the alpha zone where the vapor flux in the vacuum chamber is blocked by the mask without deposition. What is done in this area is plasma smoothing. As shown in Fig. 5, part of the mask can integrate the smoothing of the plasma to the function of doubling the plasma source in the PIAD process; that is, the plasma-assisted deposition in the beta region and the smoothing of the in-situ plasma in the alpha region. .

The momentum transfer of the plasma used for smoothing of the plasma can be determined by the following formula: Wherein n _s in the formula (3) is a substrate having a surface atomic density of, for example, a SiO ₂ deposited film in units of atoms/cm ² instead of the formula (1) CaF ₂ . This process is called in-situ plasma smoothing because the plasma interacts successively with the surface of the deposited film every 3 to 4 atomic layers.

In combination with the above three steps, the present invention describes a new method for depositing a viscous oxide film on a fluoride optical element, that is, by using an oxygen bridge to strengthen the viscous strength of the interface by correcting the momentum of the plasma. Transmission increases the packing density of the SiO ₂ film, and in-situ plasma smoothing is performed by a masking technique to reduce the defects of the coating film. Fig. 8A shows an AFM image of a CaF ₂ optical element using the F-SiO ₂ coating film of the present invention. Figure 8B shows an AFM image of a CaF ₂ optical element coated with a standard F-SiO ₂ film for comparison. The use of the techniques illustrated by the present invention, including enhanced interface chains, increased packing density, and in-situ plasma smoothing, significantly reduces the impact of substrate polishing residues on the film pattern (Fig. 8A). In other words, the standard coating process has a weaker interface chain, a lower packing density, and a higher film defect density.

Figures 9A and 9B show refractive index depth profiles of PIAD deposited F-SiO ₂ films with and without in-situ plasma smoothing at 193 nm ArF excimer laser wavelength. The depth profile is modeled by taking the ellipsoid from the film. This approach has confirmed that film volume and film surface information can be obtained (Jue Wang et al., Applied Optics, Vol. 47 (2008), pp. C189-C19). The refractive index depth profile indicates that the plasma smoothing film is homogeneous with a smooth surface (non-homogeneity <0.1%, rms = 0.29 nm), and the non-smooth film is heterogeneous to the rough surface (heterogeneity = 1.8) %, rms = 2.17 nm). The modeled surface roughness is consistent with the AFM measurements shown in Figures 8A and 8B. For example, the weak van der Waals between the CaF ₂ window and the F-SiO ₂ film produces a reduced film refractive index, a low packing density at the beginning of film deposition, and a rough surface as shown in Fig. 9B. In other words, in accordance with the present invention, the chemically bonded interface plus in-situ plasma smoothing produces a uniformly dense and smooth F-SiO ₂ coating on the CaF ₂ optical element, as shown in Figure 9A.

A 76 nm adherent and sealed F-SiO ₂ film was deposited on the CaF ₂ (111) window by the PIAD method at elevated room temperature. The cryogenic pump deposition system in the industry uses an electron gun evaporator (SYRUSpro 1110, Leybold Optics) equipped with an advanced plasma source (APS) for PIAD. The CaF ₂ window is top polished with an rms surface roughness of approximately 0.2 nm. The CaF ₂ surface is parallel to the (111) plane with an accuracy of ±2 degrees. The deposition system is low pumped to a base pressure of less than 5x10 ^-6 mbar. Low energy plasma cleaning was performed with a bias voltage of 50 V and a ratio of Ar/O ₂ gas of 1.5 before deposition. A high energy reactive plasma of 140V bias voltage is used to create a chemically bonded interface, a uniformly dense F-SiO ₂ film, and a smooth surface. The deposition rate is controlled by a 0.25 nm/s quartz monitor. During deposition, the substrate temperature and the central rotational speed of the component holder were maintained at 120 ° C and 20 rpm, respectively. Direct introduction of oxygen into the deposition chamber to establish the interface chain and maintain the correct stoichiometry of the oxide film, however argon is also used as the operating gas for the plasma source. α / β and Ar / O ₂ ratio was maintained at 3 and 2, respectively. In addition to the coating durability test according to US Militarily Standard (MIL-M-13508C section 4.4.5_abrasion/4.4.6_adhesion/4.4.7_humidity), a 193 nm ray of 40 M (million) pulses was performed at 3 kHz at 70 mJ/cm ² Shoot the test. The early failure of the F-SiO ₂ coated CaF ₂ optical element was not shown as a result of bubble formation under a 193 nm laser shot. Comparing with Figures 2 and 3, Figures 10 and 11 show optical images and SEM cross sections without early failure, such as after performing a 40M pulsed 193 nm laser at 70 kHz/cm ² at 3 kHz, in accordance with the present invention, F - Formation of bubbles of CaF ₂ optical elements of the SiO ₂ coating film. Figure 10 shows that there are no bubbles on the surface of the component/substrate 100, as seen in Figure 2. Figure 11 shows a background 45, and an F-SiO ₂ film 42 and a substrate 44 (optical element). Since the surface of the CaF ₂ coating film was peeled off as seen in Fig. 3, there was no hump in Fig. 11. The white line above the F-SiO ₂ coating is an artificially generated reflection during SEM photography, as seen in Figure 3, not because of any defects in the coating film and/or substrate.

While the invention has been described herein with respect to the specific embodiments, these embodiments Thus, it is to be understood that the invention may be It should be limited only to the scope of the following patent application.

12‧‧‧Optical components

14‧‧‧ mask

15‧‧‧Steam flux

16‧‧‧e-beam

17‧‧‧ Target

18‧‧‧ Plasma source

19‧‧‧ Plasma

20‧‧‧Deposition device

22‧‧‧Component holder

Claims (25)

A method of making an adhesive and hermetic coating on an alkaline earth metal fluoride optical component, the method comprising the steps of: providing a vacuum chamber; providing an optical component made of a single crystal alkaline earth metal fluoride in the vacuum chamber, The component is placed on a rotatable plate; at least one selected source of coating material or a mixture of coating material sources is provided, and the material is evaporated using an e-beam to provide a coating material vapor flux. a flux passing from the source of the material to the optical element in a mask having a selected shape; providing plasma ions from a plasma source; rotating the element at a selected rotational frequency f; and depositing the surface on the optical element The coating material is used as a coating film and the plasma ion impacts the film on the component during the deposition process of the material, thereby forming an adhesive and airtight film on the component; wherein: the oxide film is ≧4 eV A link energy is chemically linked to the fluoride surface of the element; the alkaline earth metal fluoride is selected from the group consisting of MgF ₂ , CaF ₂ , BaF ₂ , Sr a group consisting of F ₂ and a mixture of at least two of the alkaline earth metal fluorides; the mask being selected from the group consisting of a partial mask and a reverse mask; and coating of the optical element The coated surface has an rms surface roughness of less than 1 nm. The method of claim 1, wherein providing an optical element made of a single crystal of an alkaline earth metal fluoride means providing an optical element made of a single crystal of CaF ₂ . The method of claim 1, wherein providing at least one selected source of coating material means providing a material selected from the group consisting of Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ A group consisting of N ₄ , TiO ₂ and ZrO ₂ , and a mixture of the foregoing materials. The method of claim 1 wherein providing at least one selected source of coating material means providing a material selected from the group consisting of SiO ₂ and F-SiO ₂ . The method of claim 1, wherein the rotational frequency f is in the range of 4 to 36 rpm. The method of claim 1, wherein the rotatable plate has regions α and β, and the selected mask shape is determined by a ratio of α/β, wherein the ratio is in the range of 1 to 4. The method of claim 1, wherein the mask is a partial mask. The method of claim 1, wherein the optical component is located on the rotatable plate The optical element is coated with the coating material only on one side during the coating process. An optical component having an adhesive and hermetic coating applied to the optical component, the optical component comprising: a shaped optical component, made of a single crystal alkaline earth metal fluoride, and A coating film chemically linked to at least one light transmitting surface of the component, the coating film being bonded to the surface of the component with a chain energy of ≧4 eV. The optical component according to claim 9, wherein the molded optical component is made of an alkaline earth metal fluoride single crystal material selected from the group consisting of MgF ₂ , CaF ₂ , BaF ₂ , SrF ₂ and at least two alkaline earths. A group consisting of a mixture of metal fluorides. The optical component of claim 9, wherein the shaped optical component is made of CaF ₂ . The optical element according to claim 9, wherein the coating material is selected from the group consisting of Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ N ₄ , TiO ₂ and ZrO ₂ , and the foregoing materials a group of mixtures. The optical element according to claim 9, wherein the coating material is selected from the group consisting of SiO ₂ and F-SiO ₂ . The optical element according to claim 9, wherein one of the coating films on the optical element has a thickness in the range of 20 to 200 nm. The optical element of claim 9, wherein the thickness is in the range of 50 to 150 nm. A method of manufacturing coating film and the sealing adhesion to the method of the optical element ₂ of a CaF, the method comprising the steps of: providing a vacuum chamber; by a CaF ₂ optical element ₂ single crystal manufactured CaF, the element of the vacuum chamber Placed on a rotatable plate; providing at least one selected source of coating material or a mixture of coating material sources, and evaporating the material using an e-beam to provide a coating material vapor flux, the flux a mask having a selected shape passing from the source of material to the optical element; providing plasma ions from a plasma source; rotating the element at a selected rotational frequency f; and depositing the coating on the surface of the optical element The material acts as a deposited film, and the plasma ions impinge on the film on the component during the deposition process of the coating material, thereby forming an adhesive and airtight film on the component; wherein: the oxide film is ≧4eV a link energy chemically link to the surface of the CaF ₂ elements; the mask portion is selected from the group consisting of a mask and a reverse mask the group consisting of; the rotatable The plate has regions α and β, and the shape of the selected mask is determined by the ratio of α/β, wherein the ratio is in the range of 1 to 4; and the coated surface of the optical element has a smaller than 1 nm Rms surface roughness. The method of claim 16, wherein the mask is a partial mask. The method of claim 16, wherein providing at least one selected source of coating material means providing a material selected from the group consisting of Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ A group consisting of N ₄ , TiO ₂ and ZrO ₂ , and a mixture of the foregoing materials. The method of claim 16, wherein providing at least one selected source of coating material means providing a material selected from the group consisting of SiO ₂ and F-SiO ₂ . The method of claim 16, wherein the rotational frequency f is in the range of 4 to 36 rpm. The method of claim 16, wherein the optical element is on the rotatable plate such that only one side of the optical element is coated during the coating process Membrane material. An optical component having an adhesive and hermetic coating applied to the optical component, the optical component comprising: a molded optical component, a CaF ₂ single crystal, and a coating film The coating film is chemically linked to at least one light transmitting surface of the element, and the coating film is bonded to the surface of the element by a chain energy of ≧4 eV; wherein the coating film is selected from the group consisting of SiO ₂ and F-SiO ₂ , a group consisting of Al ₂ O ₃ , F-Al ₂ O ₃ , SiON, HfO ₂ , Si ₃ N ₄ , TiO ₂ , and ZrO ₂ , and a mixture of the foregoing materials. The optical component of claim 22, wherein the coating film is selected from the group consisting of SiO ₂ and F-SiO ₂ . The optical component of claim 22, wherein the coating film thickness on the optical component is in the range of 20 to 200 nm. The optical component of claim 22, wherein the thickness is in the range of 50 to 150 nm.